Animal nutrition involves the intake and utilization of food. Animals obtain nutrients directly or indirectly from plants. Digestion is the process of breaking down complex foods into simpler substances. Different animals obtain and ingest food in different ways such as chewing, sucking, and filtering. The human digestive system consists of the alimentary canal and digestive glands. In the mouth, teeth break down food and saliva begins to digest starches. Food then moves through the esophagus to the stomach where digestion continues, then into the small intestine where nutrients are absorbed into the bloodstream. Undigested waste moves into the large intestine then rectum and is excreted.